The present invention relates to a lens shutter driving mechanism using a lens driving mechanism.
Heretofore, a lens shutter driving mechanism is known using the lens driving mechanism in which both of a focus adjusting lens and a lens shutter are driven by a driving source constituted of a single stepping motor.
The focus adjusting operation in a single photographing operation is made prior to the shutter release operation. Accordingly, the driving mechanism of this type moves a lens driving member through a main driving member coupled through a gear with a stepping motor to a desired focused position upon the normal rotation of the stepping motor and engages the lens driving member at the focused position by means of the engagement mechanism such as, for example, a ratchet mechanism. Thereafter, the stepping motor is rotated reversely and the shutter mechanism is operated through the main driving member upon the reverse rotation of the stepping motor.
In the driving mechanism of this type, in order to control the reliable operation, it is necessary to confirm operations of the main driving member coupled through a gear with the stepping motor and the lens driving member coupled with a focus adjusting lens group.
In order to confirm the operations of both of the driving members, it is considered that positional sensors constituted of, for example, a limit switch or an photoelectric sensor are provided independently for both of the main driving member and the lens driving member.
However, there is a problem in that a cost of the sensors are high when the positional sensors are provided in both of the driving members.
In addition, since the main driving member and the lens driving member are disposed in a very small space, the provision of the two types of sensors is disadvantageous in terms of the space for the disposition.
Further, it is desired that a time lag until the completion of operation of the lens driving mechanism and the shutter driving mechanism of the automatic focusing type after the shutter button has been depressed by a photographer be as short as possible. Accordingly, when these mechanisms are operated using the stepping motor as a driving source, it is desired to shorten a period of a drive pulse for the stepping motor. However, when the period of the drive pulse for the stepping motor is shortened, the danger that the positional sensor will not effect exact detection due to chattering of the positional sensor and an attenuation characteristic in the step rotation of the stepping motor is increased. To this end, generally, an abnormal operation of the positional sensor is prevented by relative extension of the period of the drive pulse in an area in which the on and off state of the positional sensor is reversed.
In this connection, in order to ensure sufficient accuracy as the positional sensor for the driving members such as the lens driving mechanism and the shutter driving mechanism of the camera mounted in a very small space, the area in which the on and off state of the positional sensor is reversed is desired to have several steps in terms of the number of rotational steps of the stepping motor. In this manner, to ensure the several steps as the area in which the on and off state of the positional sensor is reversed is desired in terms of ensuring room for correction of an error when the error occurs at the initial position of the driving member.
Thus, when the period of the drive pulse is extended throughout the area in which the on and off state of the positional sensor is reversed as described above, a time lag until the shutter is actually operated after the shutter button has been depressed is lengthened.
It is a matter of course that if the number of steps in the area in which the on and off state of the positional sensor is reversed is reduced, the time lag can be shortened. In this case, since the state of the positional sensor is reversed while the driving member is moved in a vary small range, it is necessary to use an expensive sensor capable of detecting very small movement and room for correction of an error can be ensured wh*en the error occurs at the initial position.